1. Field of the Invention
The present invention relates to an organic semiconductor device of an arrangement wherein electrons are injected from an electron injecting electrode into organic semiconductor layers, and a method for manufacturing the organic semiconductor device.
2. Description of the Prior Art
An organic electroluminescence element, which is a typical example of an organic semiconductor device, is a light emitting element that makes use of a light emitting phenomenon that accompanies the recombination of electrons and holes in organic semiconductor layers. Specifically, an organic electroluminescence element includes organic semiconductor light emitting layers, an electron injecting electrode that injects electrons into the organic semiconductor light emitting layers, and a hole injecting electrode that injects holes into the organic semiconductor light emitting layers (see Japanese Unexamined Patent Publication No. 5-315078 (1993)).
To improve the light emitting efficiency, the electron injecting electrode must be made from a material of high electron injection efficiency, the hole injecting electrode must be made from a material of high hole injection efficiency, and a material of low work function is thus required for the electron injecting electrode.
Though from the standpoint of the work function, an Mg film is a likely candidate for the material of the electron injecting electrode, an Mg film oxidizes readily and is chemically unstable. Since an Mg film does not have a sufficient adhesive force to a base film and either is impossible to form into a film or peels off readily even if formed into a film, it is low in reliability and not fit for practical use.
Though MgAg alloys and MgIn alloys have thus been used as materials of the electron injecting electrode, with these materials, the electron injection efficiency is inadequate and separation of the electron injecting electrode occurs when continuous light emitting operation is performed over a long period of time (see Japanese Unexamined Patent Publication No. 5-315078). Moreover, an MgAg alloy is inadequate in durability against lithography processes using such organic solvents as acetone and IPA (isopropyl alcohol) and is unsuited for preparing an electron injecting electrode with a microscopic structure such as a comb-like shape.
Though Japanese Unexamined Patent Publication No. 5-315078 discloses the forming of an electron injecting electrode with a two-layer structure of an Mg layer and an Au layer on light emitting layers, a base layer to which the Mg layer can be adhered is limited, and such a structure cannot be realized depending on the type of the base layer. For example, when an electron injecting electrode is to be formed on a silicon oxide film, since an Mg layer will not adhere to the silicon oxide film, the above structure cannot be employed. Moreover, since the Mg layer is not durable against lithography processes using organic solvents, the electron injecting electrode of the above arrangement cannot be employed in a case where an electron injecting electrode with a microscopic structure is to be prepared.